Electrical space discharge tube



March 10, 1953 B. c. GARDNER 2,631,258 I ELECTRICAL SPACE DISCHARGE TUBE Filed May 21, 1947 2 SHEETS-SHEET 1' March 10, 1953 B. c. GARDNER 2,631,253

ELECTRICAL SPACEDISCHARGE TUBE Filed May 21, 1947 2 SHEETS-SHEET 2 Patented Mar. 10, 1953 ELECTRICAL SPACE DISCHARGE TUBE Bernard 0. Gardner, Waltham, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application May 21, 1947, Serial No. 749,545

8 Claims.

. This invention relates to electrical space dis- I charge tubes, and more particularly to tubes of the velocity-modulated types known as klystrons and reflex klystrons. Such tubes utilize resonant cavities, and are capable of generating ultrahigh-frequency oscillations.

It is desirable, in order to be able to cover a range of frequencies with a single tube of the above general character, to have some means for tuning or varying the resonant frequency of the 'klystron at will, thereby varying at will the fundamental frequency of oscillation.

An object of this invention is to devise a novel means for controllably tuning a cavity resonator.

Another object is to provide means for controllably tuning a klystron, said means efiectuating I a very rapid tuning of such klystron.

A further object is to devise a means for varying the resonant frequency of a klystron oscillator, which is quite simple and which requires no an enlarged scale, of a space discharge tube embodying the invention; and

, Fig. 2 is a view, similar to Fig. 1, of a modification.

Referring now to Fig. 1, the numeral I generally designates a velocity-modulated electron discharge tube of the type known as a reflex klystron.

Said tube I includes a hermetically-sealed cavity resonator 2, to which are sealed upper and lower glass envelope portions 3 and I, the interiors of parts 2, 3, and 4 communicating with each other and being sealed and exhausted in accordance with conventional practice to provide an evacuated enclosure.

Envelope portion 4 may be provided with a suitable press, not shown, at the bottom thereof, said press supporting, as by means of a stiff lead-in wire 5, a highly electron-emissive cathode 6 adapted to be heated, by means of a heater I supplied from a heating source 8, to a temperature suitable to bring about copious emission. Said cathode is surrounded by a focusing electrode 9, which is also supported from the lower press by a stiff lead-in wire III. Wire II! is connected to electrode.

the negative terminal of a battery I I, the positive terminal of which is connected to cathode lead 5, so that electrode 9 has a negative potential with respect to cathode 6.

The electron gun structure 6, 9 described above produces a compact stream of electrons which emerges through the end of electrode 9. This electron stream, whose axis coincides with the longitudinal axis of tube I, is subjected to the action of a pair of spaced electrodes I3 and I4 which are connected to. the..cavity resonator 2. Cavity resonator 2 is of generally hollow toroidal shape, as shown-is preferably made of relatively thick copper, and may be laminated, having a lower portion-2a, a ring-shaped central portion 21), and an upper portion 20, portions 2a, 2b and 20 being sealed together in the completed device.

.In order to abtract the high-frequency oscillatory energy from tube I, a window I5, madeof amaterial transparent to such energy, is sealedinto a corresponding opening provided through cavity resonator portion 21) at one side of tube I; a hollow wave-guide I6 is coupled to said opening at said window. I Lower electrode I3 is substantially frusto-conical in shape, with its smaller diameter at the upper end thereof in Fig. 1, and is integral with lower portion 2a of the cavity resonator. This electrode has a solid metallic wall but is hollow. The walls of the portion 2a are thinned toward the upper end of the electrode I3, so that at said upper end the said walls are extremely thin. The top end of the cone is cut off, so that said electrode has an axial opening extending entirely therethrough at its upper end; electrons I ca therefore travel through said electrode.

Cavity resonator portion 2c has an integral, substantially vertical cylindrical wall H, the axis of which coincides with the longitudinal axis of tube I. Electrode I4 is a very thin-walled shallow substantially cup-shaped element, the cylindrical wall I! of cavity resonator portion 20. The center of the disk wall of thecup is depressed to form a very shallow cone frustum, and an axial opening is cut through said wall, this opening being of the same diameter as the axial opening in electrode I3, and is also for the purpose'oi allowing the passage of electrons through said Electrode I4 is made of a metal or metallic alloy which has a low specific heat confrom cathode 6 through electrodes l3 and M to a point above the upper electrode l4. Due to the fact that electrode 14 has a frusto-conicatshape it forms an angle different, from 90 with the. direction of the axial linear. electron path,,which direction is vertical in Fig. 1. As a resultofLthi'sangular relationship, expansion or contraction of electrode l4, due to temperature changes thereof,

will cause corresponding downward or upward.

movement of the center'of said electrode or apex (lithe-9118; thereby correspondingly decreasing or-increasingthe distanced between the electrode elements Li. and i4 and correspondingly increas- .ingor decreasing the capacitance, between electrode elements I3; and Hi to thereby change the resonant-frequency ofiresonator 2.

The cavity resonator Z is connected, by means 0i; ahead [9,, to. the positive terminal of a battery #2, the: negative terminal of which is connected to. cathode lead 5, so. that said resonatorhas a positive. potential. with respect to cathode 6..

The electrodes; 1?. and l 4;,which are connected to each. otherv by the. cavity resonator Z, constitote an electron. velocity modul'ating electrode structure.

A metallic repeller. electrode 20' is positioned on theroppqsite side of the electrode structure 2, l3, M. from. cathodev B; electrode 29' maybe sup;- portcd, for; example at, the end ofa stifrlead-in conductor 2| integral with said" electrode and sealed through the. upper endof' envelope portion 3a, Electrode. 20 may be circular, for example, having. its center on the longitudinal axis of tube I, the diameter of said electrode being somewhat larger than the. diameter of, the axial openings in electrodes l3 and; I' l. but smaller than the diameter of. electrode [4. An annular metallic memberZZ of substantially inverted Il-shape in cross-section,.is secured'tjo electrode 20, adjacent the. lower end thereon, to provide an; annular chamber. 23 .which1 surrounds: the. bottom or actire end of. repeller electrode at. A hollow substantially toroidal cathode 24 is positioned. in chamber. 23,,with thelower suriace. ofsaid cathode. located. somewhat; above; the lower end wall of member 22. and the; lower.- end wallv of. the

smaller. electrode; 20.. propelas shown. The

' Lmveu suriaceof cathode, 24' is covered; with an electron-emissive,v coating, as indicated;

Cathode, it. is supported in position byia pair oficeramiceyelets 25 which are diametrically o.p--

through, asuitable. seal in the upper end of en- 2 velope portion. 3.. A lead-in conductor 29" is1connectedat its inner end; to the free endof heater A toroidal coil 21, and passes upwardly through the opposite eyelet 2'5 and out through a suitable seal in the upper end of envelope portion 3. Lead-ins 28 and 29 may help to support cathode 2-4 and heater 2'! in position, along with eyelets 25.

Cathode 24 is mounted adjacent electrode 20, in. such. a. position as toproiectelectrons downwardly onto electrode; lad or to cause electrons to impinge on said electrode, since the diameter of electrode 20 is smaller than that of electrode M and since cathode 24 immediately surrounds el'ectrodellll.

Lead-in 2| of repeller 20 is connected to the negative terminal of a potential source 30, the

i positiveterminal of which is connected to cathode lead 5, so that said repeller has a negative potential with respect to the cathode 6 of the electron gun. A source 3| of heating current has its opposite terminals connected to leads 28 and 29, to supply heating current to heater 2].

The annular chamber 2 3" houses the cathode 24' wells defining; this chamber areelectrically connected to the repell'er 29, sothat electrically, as" Well as' physically; a' portion of electrode 20 partially surrounds said cathode. A source of bias potential 32 has" its negative terminal connected to repeller lead 21", and amovable tap 33 on said source" isconn'ected to cathode-lead 2 8, so that; in effect, a potential negative-with respectto" cathode 25- is" applied to-r-epeller 2'85; the amount of this negative bias can be varied. by movement of tap-33; The-walls'defining chamber 23' serve as a" grid, to control the fl'ow' of electrons between cathode 2 i and electrode M, the flow dependingon the voltage applied; from source- 32, between cathode 2d and electrode 29.

When the tube l isenergized by potentials; as above described; from sources 8-; 2-, and 35., a beam of" electrons coming from the" cathode 5 will be accelerated by the accelerating electrode 9, and" pass through: the electrodes i3 and M of cavity resonator 2. As: the beam emerges from the electrode It, it is reflected by the repeller electrode 29" back" through" the pair of electrode elements. l3and Hi; As is wellknown, the initial passage. of' the beam" through" the electrodes I3 and. M produces :a. bunching action, and, upon reflection and repassage oi" the beam through these electrodes,- a debunching action results, which. feeds ultra-highefrequency energy tothe resonant circuit formed by; the cavityresonator 2', thus setting up ultra-highrfrequency oscillations, of. a frequency determined by'the'crelative dimensions of said resonator; which. maybe; ab-

stractedby waveguide. 1.6.

By changing'the spacing between elements; l3 and. [4, that is; bychangi'ngthe. gap length a, the resonant; frequency" of' resonator-- 2* may" be varied; in other words, by so doing, the tube l maybe tun'e'di When heater 2-! is energizedfrom source. 3!, cathode 2s" emits electrons. Thereis normally a high. potential. between cathode 24 and; electrode Id of the cavity resonator; said electrode'being positive with respect'to' said cathode; this can. be seenfrom the-fact that repeller 20' is negativev with respect to cathode 6 and cavity resonator Zis highly positive with respect to said cathode, while cathode-21l is only slightly positive with respect to repeller' I28. Electrons from cathode 24' therefore strike electrode [4 trode, by'varying" the potential applied between klystron I, may be controlled.

' omitted. 'merals are used to refer to parts the same as said cathode and repeller electrode z ll'. Thetem' perature of electrode I4 is increased in proportion "to the number and energy of the electrons impinging upon it.

As the temperature of electrode l4 increases, it expands asubstantial amount, due to its substantial thermal coefiicient of expansion; this expansion produces a downward movement at the apex of the cone, due to the angular relation of said electrode and the electron path, as explained above. The downward movement decreases the gap spacing or length a, increasing the capacitance provided by said gap and lowering the resionant frequency of resonator 2, thus lowering the oscillatory frequency of the klystron I.

When fewer electrons, or electrons of lower energy content, impinge on electrode I4, the temv perature of said electrode drops, causing shrinkage thereof, increasing gap length a and raising the frequency of the oscillations.

The electron flow between cathode 24 and electrode I4 is controllable by controlling the poten tial appliedbetween said cathode and electrode 20 by moving the tap 33 on source 32; thus, by

controlling this potential, the temperature of electrode l4, and therefore also the frequency The entire upper portion 20 of cavity resonator '2, except for electrode I4, is made of relatively thick copper which is brazed to the copper portion 2b of the resonator. Since electrode l4 has low heat conductivity, and, since this copper portion has high heat conductivity, there is relatively small temperature variation of resonator section 20 as electrode I4 is varied in temperature. From all of the above, it will be seen' that I have devised a novel, thermal, means for con- "trollably tuning a cavity resonator. It has been 'found that, with this invention, frequency changes of a klystron may be effectuated in time intervals on the order of a half-second or less, 1 since the electrons act directly on electrode M of the cavity resonator, and not through any linkage mechanism.

Cavity resonator 2 is hermetically sealed, andthe entire interior of said resonator is evacuated. Upper glass envelope 3 may be sealed to an annular wall 34 projecting upwardly from the upper exterior surface of resonator 2, while lower glass 'envelope 4 may be sealed to a similar annular wall 35 projecting downwardly from the lower exterior surface of said resonator. Therefore,

{cavity resonator 2 and envelopes'3 and 4 provide an evacuated enclosure.

Now referring to Fig. 2, a modification is shown by means of which the upper cathode may be In this figure, similar reference'nuthose of Fig. 1.

Repeller electrode 36 has a longitudinal axial aperture 31 extending entirely therethrough, and supported in this aperture, but insulated from electrode 36-by means of a vitreous disk 38 near the lower end of said aperture, is a rod-like electrode member 39. Electrode 36 and member 39 both pass out of the evacuated enclosure, being sealed through the top wall of upper envelope portion 3.

The positive terminal of a bias potential source 40 is connected to repeller electrode 36, and a movable tap M on said source is connected to member 39, so that a potential, negative with respect to repeller 36, is applied to said member; the value of this negative potential can by movement of tap 4|. I

be varied T6 In the device of Fig. 2, it has been found that the electron stream'from the regular klystron gun 6, 9 can'be area-modulated in the repeller zone by a potential applied between repeller 36 and member 9. In other words, the cross-section of the stream, on its return trip from-the repeller zone back through electrodes l3 and H, can be varied by varying the potential between member '39' and repeller 36. It has been found that the electron stream will be spread more as the member 39 is made more negative, and that the potential of said member will'determine the amount of spread of the stream.- As the stream is spread, some of the electrons therein will impinge on electrode 'Hi, the number of electrons so impinging jdepe'ndin'g on the amount ofspreading'of the stream, and therefore'on the potential applied' to member'39.

The electrons which i "pinge on electrode will do so with sufiicient velocity'and in sufficient numbers to raise'the temperature of said electrode, thus producing a thermal tuning action as in Fig. 1. The action may be controlled by controlling the potential applied to member 39,'in this manner controlling the'temperature'ofelec trode M by controlling the electron flow impinging thereon. thereby also controlling the frequency of klystron l-accordingly. v v v Of course, it is to' be understood that this invention is not limited to the particular details "as described above, as many equivalents will su gest themselves to those skilled in the art. For example, instead of depressing the central portion of electrode l4 so that the apex of the cone points downwardly, the central portion of said electrode may be raised, in which case a frequency variation with electron flow opposite to that described above would be eifectuated. Various other variations will suggest themselves; It is ac- 'cordingly desired that the appended claims'b'e given a broad'interpretation commensurate wit the scope of this invention within the'art.

What is claimed is: 1

f 1. An electron velocity-modulation discharge tube, comprising a plurality of electrodes including an electron-emissive cathode, an electron velocity-modulating electrode structure comprising a pair of spaced electrode elements through which an electron path from said cathodepasses,

said electrode elements being connected to each trollable means comprising electron directing electrode means adjacent said elements for causing electrons to impinge on said deformable element.

2. An electron velocity-modulation discharge tube, comprising a plurality of electrodes including an electron-emissive cathode, an electron velocity-modulating electrode structure comprising pair of spaced electrode elements between and through which a linear electron path from said cathode passes, a portion of one of said electrode elements forming an angle with the direction of said path, said angle being different from'ninety degrees-whereby variations in the '-'-temperature of said portion will produce :varia- 'tions in the length of the portion of said path between said electrodepelements. said electrode assigns.

:fliflhlfllltfit being; to each; other and forming nartsof the walls. oi m cavity; resonaton;

electrons. directing; electrode means adjacent saith elements; for: causing cl'ectrons:-- to impinge unomsa-idmortionaion warning, thetemperatures);

said-L condom of; saidacne; electrode-elemental.

31. electrons uelocitn-modulation.- dischar e tube; comprising; a. plural-rim oi electrodes: includ ingrlam elcctron-emissivee cathode, an: electron:

.uclocityamodulating; electrodes structure: comprisr a; pai-rrofi spaced; electrode. elements; between.

and. through which. a; linear electron path.v from saidcathodernasses; arportiornof onerof saidelec- .trode. clementszfiorming, am angle; the. direct.-

tiOlizOLSflidl path, said; angles; being. different from ninety (leafless-said. portion. having; an.- aggreciabie thermal coefiicieme ofi expansion; whereby variationsin. the temperature of said gortior-rwill.

grodiuce: substantialavariations inc the lengths of the portiom 01 said; patio betwecnaqsaid; electrode. elements. saith. electrode elements being con:-

nectethtd eachlothers and forming. part ofi. the.

walls of. a cavity resonators. and contnollable.

electron. directing: electrode. means. adjacer-ittv said elements for: causing. electrons to impinge; upon said? portion. tor-vary g; the-temperature: Gfi said .gortiomot saidone: electrode: element...

4'; An electron velocitymodulationx discharge tube, comprising; at pluralitn of electrodes. includana eIectron-emissivecathodes. an.v electron. venom-modulating.electrode structure: comprisa, air of. spacedselectrode elements between and through-.- whiclt a. linear: electron. path from saidcathode. passes. atleasha portionrot one. of said: electrode; elements forming; an. angle-. with the. direction. of said: path; said -anglebeing-difier- .ent from ninety; degrees wherebw variations: in thetemperature; of; said portion. will oroduce .variations; im the. lcngtln of. the portion... of. said path between. said electrode elements, said elec.

;trode elements; being, connected to": each other. by

a cavity resonator having. a. resonant frequency dependent on the length & saidrportioniof; aid

'path an additional: electrode on: the opposite side of;saidtelectrodelstructure.from saidcathode,.

as second electroneemissiuecathode. mounted adjacent-said additionalelectrode tozprojectlelectrons onto said; portion. of, said one electrode 1 element,v means adiacentt said portion: for. causing impingement/0L. said. electrons. onsaid. portion... of

saidoneelectrodeeelement withsuflicientlvelocity to raises the temperature: thereoLi. a oortion of said. additionall electrode nartialhc-surroundin saidsecond; cathode for: .controllin the: electron flow; between; second. cathode; nd' said. por-- 'tion; 02 said one.) electrode.-ele1nent, .byrthe control" 'ofi the-voltage applied; between saicflisecond; oath.-

. ode: additional; electrodes electron velocity-modulation discharge tube,,.c omprising. a; plurality.- of. electrodes-including... electron-emissive cathode.,. an electron vel'ocity modulating electrode structurecompris- ,ing: a. pair of; spaced.. electrode elements between and. through. which a. linear electron. path from said cathode. atlleastalgortion of: onelof.

, said electrode elements; forming, an. angle; with thedirectionlof; said-.gathesaidflangle being; dimerent from. ninetn degrees, said; portion having; a

substantial. thermal. coefiicient of expansion whereby variations the temperature oi. said. portion wilt. roduce substantial: variations in; the lengtlr of the portiom of; said; oath between said.

. electrode:- elements;v saith electrode; elements being 2 connected-i. ten each;- other: ascauitw resonator a resonant cm the .lengtlnof. said.- portionoLsaidpath, anadditional electrode on the opposite side. of'jsai'd" electrode structure; fromv said cathode, and. a... second. electron-emissive cathode mounted adjacent said ad.- ditional, electrode to.- project. electrons. onto, said portionsofi said. one: electrodeel'ement, meansQadiacent said portion, tor causing, impingement. of

said electrons on.- said portion. oft said. one electrodezelementcwith;sufificient velocity) to... raisev the temperaturethereof;.a..portion of said additional electrode partiallysurrounding. said second'cathodefor controlling. the electronsfiow between said second cathodeand said. portionof said; one electrode;- element, by the; control. of the. voltage applied between. said cathode and. said; additional electrode.

Y 6;- An electron;v velocity-modulation discharge tube... comprising; a: plurality? of electrodesincluding:- an electronlemissivecathode5. an electron velocity-modulating, electrode... structure. comprising a.. pair:- of. spaced-electrode. elements between and through which a" linear electron. path. from saidcathode passes the.porti0n.of oneof said electrode elements; adj acent saidpath: forming an angle. with. the direction of said path,v said. angle being. different. from, ninety degrees, whereby variations in the tempcratu-reofi said portion. will produce. variations in the. length of the. portion of said. path. between said; electrode elements,

- andthroH- which. a linear electron path; from said cathode passes, the portion of. one. of said electrode. elements; adjacent. said path. forming an, angle. with; the. direction of. said path, said angle. being: di-fl'erent from. ninety, degrees. said I portion: havingfan. appreciable.thermalcoeflicient I or: expansion whereby variationsinthe temperatureoi saidportion will produce substantial variationslthe-lengthot the; portion of said path bemoan: said. electrode elements said...electr.o.de

. elementsbeing connectedltow each other by; and

forming part of theJwa-lls-of, alcalvity resonator,

additional; electrode on: the. opnosite side of a electrode; structuraironr said. cathode and adantejditol-refiect-the electron; stream from; said cathode. back: through said electrode. structure, and an electron directin electrode adjacent said additional electrode. for." spreading, said; stream whereby some. of the? electronstherein impinge on; said portion of said. one. electrode. element witlnsuflicient velocity to, raise the; temperature thereon.

8. An electron: uelocityr-modulationv discharge tube, comprising. a plurality of electrodesdncluding. an electron-emissiue cathode an electron velocity-modulating electrode structure comprising. a of. spaced electrode.- elements. through c which an electron-path-from, said cathode passes,

said;- electrode: elements being connected; to. each other by and f orming QEIZB ct. thewallse oiarcauity resonator-x; one oi; said; electrode. elements: being thermally defonnable andgirustroz-conicahto produce variations in the distanceebetweensaidelcetrode elements in response to variations in the temperature of the same, and controllable means adjacent said elements for varying the temperature of said one electrode element to vary said distance, said controllable means comprising electron directing electrode means adjacent said elements for causing electrons to impinge on said deformable element.

BERNARD C. GARDNER.

REFERENCES CITED UNITED STATES PATENTS Name Date Ruben Apr. 22, 1930 Number Number 10 Name Date Varian et al July 29, 1941 McArthur May 26, 1942 Haeff Apr. 23, 1946 Snow Oct. 8, 1946 Rochester Dec. 17, 1946 Varian et a1 Jan. 21, 1947 Harrison et a1. Jan. 21, 1947 Quitter Oct. 21, 1947 Clifiord et a1. Nov. 23, 1948 Ekstrand et al Jan. 17, 1950 Ekstrand et a1 July 4, 1950 Pierce July 4, 1950 

